1. Field of the Invention
This invention relates to a high temperature microscope and, more particularly, to a high temperature microscope including a peep window provided in a chamber.
2. Description of the Prior Art
There has been known a high temperature microscope comprising an optical system and a chamber system, in which an object to be observed is accommodated in a chamber having a peep window and capable of controlling at least either temperature, atmosphere and ambient pressure for observation of the object at a high temperature with the object and peep window positioned such that they cross the optical axis of the objective lens of the microscope. While this high temperature microscope is used to observe the object at a high temperature, vapor generated from the object is deposited on the inner or back surface of the peep window, which is thus fogged to become opaque in a short period of time. Therefore, it is no longer possible to continually observe the object. To avoid this, there has been proposed a high temperature microscope, in which there are provided a peep window capable of rotation about an axis parallel to and spaced apart from the optical axis of the objective lens and means for causing intermittent frictional rotation of the peep window to bring the opaque portion thereof out of the optical axis of the objective lens and bring a transparent portion to the position on the optical axis.
Also, there has been proposed another high temperature microscope, in which there is provided a thin transparent member disposed between a stationary peep window and an object to be observed for rotation about an axis extending parallel to and spaced apart from the optical axis of the objective lens such that vapor generated from the object is deposited on the transparent member to prevent vapor from being directly deposited on the peep window, the transparent member being intermittently frictionally rotated to bring the opaque portion of the transparent member resulting from vapor deposition out of the optical axis and bring a transparent portion to a position on the optical axis, thus permitting observation of the object through the peep window and transparent portion of the transparent member for a long time.
In the former one of the above two high temperature microscopes, the peep window is intermittently rotated about an axis extending parallel to and spaced apart from the optical axis to successively move a portion of the peep window which has become fogged and opaque due to vapor deposition during the observation of the object, thus permitting extending a time capable of observation to a certain extent. However, when the peep window is rotated by one rotation to that the initial portion of the peep window comes to the optical axis, this portion is opaque because the entire annular portion of the peep window is opaque. Therefore, no further observation of the object can be made.
When observing an object with a high temperature microscope, the ambient pressure in the chamber is controlled between a vacuum and a high pressure. Therefore, the diameter of the peep window can not be made very large from the standpoint of the pressure resistance. Also, the thickness of the peep window can not be made very large from the optical standpoint. That is, the peep window has to be as thin as possible and has as small diameter as possible. With a microscope having such a peep window, only several transparent portions at the most may be successively brought to a position on the optical axis for continuous observation by intermittently rotating the opaque portion of the peep window. This means that observation of an object of high vapor pressure or an object of low vapor pressure, i.e., pure iron, at a high temperature of 1,000.degree. C. only for one minute.
In the latter high temperature microscope, in which the rotatable transparent member is provided between the peep window and the object, like the former high temperature microscope, an annular opaque portion of the transparent member is formed when the transparent member is rotated one rotation during observation. When this results, no further continual observation can be made, that is, the period, during which continuous observation can be made, is short like the former high temperature microscope. Further, with this high temperature microscope harmful reflected light is liable to be produced from the upper and lower surfaces of the transparent member during observation. Further, the transparent member must be made very thin. Therefore, it is difficult to make both the upper and lower surfaces of the transparent member smooth, and deterioration of the optical performance is prone. In order to solve the above-mentioned defects, the present inventors previously proposed a method of observing a metallic structure with a high temperature microscope to enable to observe the structure for an extended of time under a high vacuum and a high temperature by Japan Patent Laying Open Publication No. 59-31440/84 and read a paper on the subject at Proceedings of Fourth Japan Institute of Metals International Symposium held on Nov. 25-29, 1985.